In the manufacture of a hollow-fiber membrane filter element, a two-liquid mixing type epoxy resin or urethane resin is typically used as a potting material (fixing agent) in order to adhere and fix hollow-fiber membranes and thereby form a partition portion. During formation of the partition portion, constituents of the adhesive, that is, a base and a curing agent are measured and mixed and then, the resulting mixture is injected into the space between hollow-fiber membranes within a time while it has fluidity.
Hollow-fiber membrane filter elements are used in many fields such as various industrial processes, production of drinking water, and sewage treatment. In many cases, filter elements having a diameter of from 80 to 300 mm are used. For manufacturing such a relatively large-sized filter element, a adhesive curable within a period of time short but enough to complete a bonding operation and capable of achieving high productivity is preferred. A adhesive having a pot life TP of from 5 to 60 minutes is often employed.
A adhesive for forming a partition portion of a hollow-fiber membrane filter element is apt to cause inadequate mixing because miscibility between a base and a curing agent is not good due to poor compatibility therebetween. Accordingly, there sometimes occurs unevenness in the cured state of the adhesive. For injecting the mixture between hollow-fiber membranes, it is the common practice to employ static potting method of injecting the mixture while utilizing a head differential or pump pressure and a centrifugal potting method of injecting the mixture by utilizing a centrifugal force. The latter centrifugal potting method is preferred because it facilitates formation of a uniform interface. In the centrifugal potting method, when the miscibility between a base and a curing agent is poor, partial unevenness in the mechanical strength after curing (which will hereinafter be called “curing unevenness”) is apt to occur due to separation of the adhesive into two layers by the centrifugal force. In the hollow-fiber membrane filter element, the partition portion has a function of keeping pressure resistance so that presence of curing unevenness is a serious problem leading to inferior quality of the filter element as a product.
The constituents of a two-liquid mixing type adhesive are mixed, for example, by a method of rotating a stirring blade in a vessel or by a method of feeding them into a static mixer with a pump. A method of mixing them in a disposable static mixer is preferably employed because it does not need washing after use. When a static mixer without mixing elements is used, however, the constituents cannot be mixed uniformly and the resin obtained by the reaction tends to have curing unevenness. When a static mixer is equipped with many mixing elements in order to attain sufficient mixing, on the other hand, feeding of a mixed liquid requires a very high pressure.
Since a disposable static mixer is typically made of plastic, only a low pressure can be applied to it. In order to mix the constituents within a usable pressure range, mixing must be performed at a low flow rate and it takes long hours to obtain a predetermined amount of the mixture. This makes it difficult to complete the bonding step within the pot life of the adhesive.
With a view to overcoming the above-described problem, Japanese Patent Application Laid-Open No. Hei 5-31426 (Patent Document 1) discloses, as a method of using a disposable static mixer under high pressure, a method of sandwiching the outer portion of the disposable static mixers with metallic holders and connecting the static mixers with a metal block. This method however has problems such as necessity of a disassembly or assembly work of the holders whenever the static mixers are used and excessively high energy consumption for feeding under high pressure.
Patent Document 1: Japanese Patent Application Laid-Open No. Hei 5-31426